The U.S. fertility rate has taken a nose dive and why is a complete mystery

The effect of this trend will be with us for decades to come, experts say.

The declining U.S. fertility rate increases need for immigrant workers. (Image credit: Getty Images)

Governments in Western Europe, Russia, and East Asia have long worried about their dropping birth rates. They’re concerned about replacement, the idea that they need a certain number of young people working to support seniors reliant on government’s social systems. Recently, the U.S. has joined them. Economists also fear a lack of young, strong, talented workers to replace those entering retirement might even slow down economic growth.


The latest figures show a record low birth rate last year, for the second straight year in a row. The trouble is, researchers aren’t sure why. In 2017, there were a mere 60.2 births per 1,000 women of childbearing age (ages 15-44). That means the overall fertility rate dropped 2% from 2016. This is the lowest level since 1978. These figures come from the National Center for Health Statistics.

Demographers there collected birth data from all across the country, along with the year’s birth certificates. This is the largest single drop since 2010, during the worst period of the Great Recession. There was a tiny increase in 2014, but that year stands out as an anomaly. Overall, there’s been a downward trend for decades, meaning the number of births aren’t enough to replace the declining population.


The US birthrate has been dropping steadily for decades. But last year’s figures show the steepest decline yet. (Image credit: Getty Images.)

Demographers aren’t surprised. Most developed countries are seeing the same thing. However, they’re stymied as to what’s driving the downturn in America. Usually, hard economic times cause a drop in the birth rate while an improved economy sees a rise. The Total Fertility Rate (TFR), or how many births a woman bears in her lifetime, should be at an optimal rate of 2.1. Today, it’s 1.76 per woman. What’s more shocking is that the rate has declined, even though there are more women of childbearing age around today than in decades past.

If you look at TFR over the course of the last century, you can get a good sense of how it’s changed over time. In the early years of the 20th century, TFR was around 3 per woman. Keep in mind too that childhood diseases also took out lots of kids before they reached maturity. In the 1940s with prosperity and penicillin, that number leveled off to about 2.1.

The post-war period of course saw a baby boom, where the TFR peaked at 3.7. Afterward, it declined over decades to a stable 2.1 in the 1970s. Of course, greater prosperity often equates to a lower TFR. But too low a total fertility rate, and a country finds itself in trouble.

Besides replacement, are there other reasons this decline is noteworthy? Co-author of the report Brady E. Hamilton told Buzzfeed, "This information allows you to better understand what your population will look like in 10 or 20 years so you can forecast what the workforce would look like, demand for educational facilities, and resources." For instance, this drop in TFR is thought to impact social security and Medicare for the next few decades.


One reason may be, women in developed countries are focusing more on their career and putting off having a family. But demographers say this isn’t the full story. (Image credit: Getty Images.)

There are some indications of what might be causing this trend. For instance, women today are postponing marriage and having a family for longer stints in higher education and to build up their career. Women are more likely to have children past the age of 35 nowadays than in times past. Long-term contraception might also be a factor.

Are stagnant wages playing a role? Inflation keeps rising, while for years wages have hardly inched up. Consider how much it costs to raise a child, over $200,000 in the U.S. just to the age of 18. That's quite a bit, especially for millennials and Gen-Xers, the majority of which are still living paycheck to paycheck. 

There was one bright spot: teen births declined 7%. Also, the U.S. still has a higher birthrate than other developed countries. Even so, these numbers make it official, the US is an aging society, which is particularly impactful due to the large size of the aging baby boomer generation. The fact that people live longer nowadays than ever before doesn’t help matters, either. Demographers say this decline will likely continue. As a result, the U.S. won’t be in fiscal health without a steady stream of immigrant workers to replace workers lost to the dropping fertility rate.

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Image source: Vaccaro et al, 2020/Harvard Medical School
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We don't have to tell you what it feels like when you don't get enough sleep. A night or two of that can be miserable; long-term sleeplessness is out-and-out debilitating. Though we know from personal experience that we need sleep — our cognitive, metabolic, cardiovascular, and immune functioning depend on it — a lack of it does more than just make you feel like you want to die. It can actually kill you, according to study of rats published in 1989. But why?

A new study answers that question, and in an unexpected way. It appears that the sleeplessness/death connection has nothing to do with the brain or nervous system as many have assumed — it happens in your gut. Equally amazing, the study's authors were able to reverse the ill effects with antioxidants.

The study, from researchers at Harvard Medical School (HMS), is published in the journal Cell.

An unexpected culprit

The new research examines the mechanisms at play in sleep-deprived fruit flies and in mice — long-term sleep-deprivation experiments with humans are considered ethically iffy.

What the scientists found is that death from sleep deprivation is always preceded by a buildup of Reactive Oxygen Species (ROS) in the gut. These are not, as their name implies, living organisms. ROS are reactive molecules that are part of the immune system's response to invading microbes, and recent research suggests they're paradoxically key players in normal cell signal transduction and cell cycling as well. However, having an excess of ROS leads to oxidative stress, which is linked to "macromolecular damage and is implicated in various disease states such as atherosclerosis, diabetes, cancer, neurodegeneration, and aging." To prevent this, cellular defenses typically maintain a balance between ROS production and removal.

"We took an unbiased approach and searched throughout the body for indicators of damage from sleep deprivation," says senior study author Dragana Rogulja, admitting, "We were surprised to find it was the gut that plays a key role in causing death." The accumulation occurred in both sleep-deprived fruit flies and mice.

"Even more surprising," Rogulja recalls, "we found that premature death could be prevented. Each morning, we would all gather around to look at the flies, with disbelief to be honest. What we saw is that every time we could neutralize ROS in the gut, we could rescue the flies." Fruit flies given any of 11 antioxidant compounds — including melatonin, lipoic acid and NAD — that neutralize ROS buildups remained active and lived a normal length of time in spite of sleep deprivation. (The researchers note that these antioxidants did not extend the lifespans of non-sleep deprived control subjects.)

fly with thought bubble that says "What? I'm awake!"

Image source: Tomasz Klejdysz/Shutterstock/Big Think

The experiments

The study's tests were managed by co-first authors Alexandra Vaccaro and Yosef Kaplan Dor, both research fellows at HMS.

You may wonder how you compel a fruit fly to sleep, or for that matter, how you keep one awake. The researchers ascertained that fruit flies doze off in response to being shaken, and thus were the control subjects induced to snooze in their individual, warmed tubes. Each subject occupied its own 29 °C (84F) tube.

For their sleepless cohort, fruit flies were genetically manipulated to express a heat-sensitive protein in specific neurons. These neurons are known to suppress sleep, and did so — the fruit flies' activity levels, or lack thereof, were tracked using infrared beams.

Starting at Day 10 of sleep deprivation, fruit flies began dying, with all of them dead by Day 20. Control flies lived up to 40 days.

The scientists sought out markers that would indicate cell damage in their sleepless subjects. They saw no difference in brain tissue and elsewhere between the well-rested and sleep-deprived fruit flies, with the exception of one fruit fly.

However, in the guts of sleep-deprived fruit flies was a massive accumulation of ROS, which peaked around Day 10. Says Vaccaro, "We found that sleep-deprived flies were dying at the same pace, every time, and when we looked at markers of cell damage and death, the one tissue that really stood out was the gut." She adds, "I remember when we did the first experiment, you could immediately tell under the microscope that there was a striking difference. That almost never happens in lab research."

The experiments were repeated with mice who were gently kept awake for five days. Again, ROS built up over time in their small and large intestines but nowhere else.

As noted above, the administering of antioxidants alleviated the effect of the ROS buildup. In addition, flies that were modified to overproduce gut antioxidant enzymes were found to be immune to the damaging effects of sleep deprivation.

The research leaves some important questions unanswered. Says Kaplan Dor, "We still don't know why sleep loss causes ROS accumulation in the gut, and why this is lethal." He hypothesizes, "Sleep deprivation could directly affect the gut, but the trigger may also originate in the brain. Similarly, death could be due to damage in the gut or because high levels of ROS have systemic effects, or some combination of these."

The HMS researchers are now investigating the chemical pathways by which sleep-deprivation triggers the ROS buildup, and the means by which the ROS wreak cell havoc.

"We need to understand the biology of how sleep deprivation damages the body so that we can find ways to prevent this harm," says Rogulja.

Referring to the value of this study to humans, she notes,"So many of us are chronically sleep deprived. Even if we know staying up late every night is bad, we still do it. We believe we've identified a central issue that, when eliminated, allows for survival without sleep, at least in fruit flies."

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